For many neurodegenerative diseases, both effective treatments and underlying causes are unknown. A specific protein, TDP-43, has recently been shown to be abnormally deposited in multiple neurodegenerative diseases, including Amyotropic Lateral Sclerosis (ALS) and Frontotemporal Lobar Dementia (FTLD). TDP-43 (TARDBP) is a conserved, broadly expressed nuclear protein with demonstrated roles in mRNA splicing and stability. By analogy with other neurodegenerative diseases associated with specific protein inclusions or aggregates (e.g., huntingtin in Huntington's, 1-synuclein in Parkinson's, 1-amyloid peptide in Alzheimer's, etc.), there are good reasons to believe that TDP-43 plays a causal role in neurodegenerative pathology. We have expressed human TDP-43 in C. elegans in order to assess the effects of TDP-43 overexpression in an in vivo model. Our experiments show that transgenic worms with neuronal expression of human TDP-43 have an uncoordinated movement phenotype that is indicative of neuronal dysfunction. Thus, our data support a neurotoxic role for TDP-43. The molecular mechanism(s) by which TDP-43 may be neurotoxic are unclear, in part because the full range of TDP-43 function is unknown. TDP-43-positive inclusions occur in FTLD cases caused by loss-of-function mutations in progranulin but the biological connection between TDP-43 and progranulin has not been established. In this project, we will seek to identify the conserved functions of TDP-43 (and progranulin), and the molecular and cellular mechanisms by which TDP-43 causes neurodegeneration. Specifically, we will carefully characterize C. elegans strains with deletions of TDP-43 and progranulin to determine the functions of these genes at the organismal level. We will also generate and characterize a series of transgenic C. elegans strains expressing variants of human TDP-43 designed to elucidate the molecular mechanisms of TDP-43 toxicity. These transgenic strains will also be used in forward genetic screens to identify components of the TDP-43 neurotoxic pathway. The C. elegans studies will be complemented by parallel cell culture studies, which will serve to validate and extend findings made in the C. elegans model system. PUBLIC HEALTH RELEVANCE: For many neurodegenerative diseases, both effective treatments and underlying causes are unknown. A specific protein, TDP-43, has recently been shown to be abnormally deposited in multiple neurodegenerative diseases, including Amyotropic Lateral Sclerosis (ALS) and Frontotemporal Lobar Dementia (FTLD). In this project we will use model systems to determine the functions of TDP-43 and how its deposition may cause neurodegeneration.